The invention relates to a shoe and leather care product, in particular a shoe and leather polish, to a process for preparing a shoe and leather care product and to the use of said shoe and leather care product for treating or cleaning shoes. More in particular, the invention relates to a shoe and leather care product having a reduced content of organic components, i.e. a low volatile organic content (VOC).
When the term shoe care is used in the context of the present invention it is intended to include both shoe and leather. Unless otherwise indicated herein, all percentages are percentages by weight calculated on the basis of the weight of the total shoe or leather care product.
The state of the art of the art of shoe care products, such as shoe polish, is well summarised by Peter A. Burke in Ullmann's encyclopaedia of Industrial Chemistry, Sixth edition, 2000 Electronic release on Shoe Polishes. Shoe care products are colourless or coloured pastes or fluids containing a wax phase. They are typically applied by polishing onto the leather surface of footwear such as shoes to provide a wax layer having a high gloss. Simply said, there are two classes of shoe care products: those that are oil based, and those that are based on an aqueous phase (emulsion based products).
Examples of oil based shoe care products are shoe creams and shoe polishes. A shoe polish typically consists of a mixture of waxes, such as Crude Montan wax and modified forms thereof (e.g. acid waxes, ester waxes and partly saponified waxes), Fisher Tropsch waxes and modified forms thereof (e.g. oxidised Fisher Tropsch waxes and partly saponified Fisher Tropsch waxes), polyethylene waxes and modified forms thereof (e.g. oxidised polyethylene waxes), metallocene waxes, micro waxes, ceresin, carnauba wax, candelilla wax, stearic acid, or synthetic waxes, and a mixture of solvents, such as terpene oil, mineral spirits, white spirit, aromatics free/desaromatized white spirit and the like. Oil based shoe care products are relatively hard and have a good consistency allowing an easy application to the leather.
Shoe care products based on an aqueous phase are most often made available in the form of paste or cream-like emulsions in tubes or jars, or in the form of fluids in bottles. Thickened emulsions are also known and are sold in tins or glass jars.
In the last decade environmental, toxicological and cost considerations have stimulated research into so called Low VOC Polishes. These are shoe polishes having a low (or no) content of organic solvents. The environmental considerations causing concern for volatile organic compound are rooted in ozone creating potential for these compounds and global warming. The toxicological concerns are based on the alleged risks of volatile organic compounds to human health.
In Europe as well as in the US, the use of volatile organic solvents (VOCs) is regulated. In Europe, a volatile organic compound is a compound that has a starting boiling point lower than 250 degrees Celsius at atmospheric pressure. For working environments volatile organic compounds are defined as having a vapour pressure equal to or larger then 0.01 kPa at 293.15 Kelvin. Originally in the United States VOCs were defined as volatile organic compounds having a vapour pressure of 0.1 mm Hg or larger at 70 degrees Fahrenheit. Currently an exempt list is used based on proven negligible photochemical reactivity. Within the scope of this invention a VOC is defined as a volatile organic compound that has a starting boiling point lower then 250° C. at atmospheric pressure.
High crude oil cost price during the oil crises in the past decades has furthermore created the need for formulae that are less dependent on crude oil cost price that determines the cost of petroleum distillates used in paste shoe polish like mineral spirits, kerosene, Varnish Makers and Painters Naptha, Stoddard solvent, white spirit and aromatics free/desaromatised white spirit.
Organic solvents in solvent-based shoe polishes have multiple basic functions. They assist in achieving ease of application (ease of spreading of the product and ease of buffing) of the product. They assist in achieving maximum liquefaction during application. They perform a role in cleaning the leather and in driving the waxes and oils present in the shoe polish into the pores of the leather. They ensure that any remaining wax layers of previous treatments are redissolved and also that the wax component is solubilised in the product. They further plasticise and soften the wax and facilitate removal of excess wax applied. They provide for an adequate evaporation rate, adequate product structure and stability to ensure adequate shelf life in terms of solvent retention, absence of solvent syneresis, phase separation and the like. They furthermore contribute to product consistency, weight stability and product performance stability.
All of these functions provide and support the raw materials in the product in achieving desirable surface gloss, depth of gloss, gloss durability, cleaning, nourishing, conditioning, protecting, colouring and waterproofing properties of a shoe care product. Upon reduction or removal of solvents, all these various functions have to be provided for by balancing other components in the product to ensure and retain consumer satisfaction with the current product paste shoe polish.
Basically, the only realistic alternative to reduce the level of organic solvent is to exchange organic solvent with water. Water can be introduced as an external or water continuous phase in terms of an (o/w), or oil-in-water emulsion, an internal discontinuous phase in terms of a water-in-oil emulsion, also called inverse emulsion, also called oil continuous or w/o emulsion, or a mixture of the two afore mentioned approaches with a water continuous phase w/o/w emulsion or a multiple phase emulsion. In the context of the present invention, any emulsion belongs either to the class of the oil continuous emulsion systems or the class of the water continuous emulsion systems.
Clearly the state of the art of oil continuous emulsions (w/o) is such that in today's competitive environment manufacturers still are forced to revert to non-emulsion white spirit based formulation technology. Thus, producers, due to consumer preferences for white spirit based technology, do not employ oil continuous shoe polish emulsion technology.
Known problems with shoe care products of this type include the consistency of the product being too thick and thereby affecting the ease of application and spreadability of the product, drying out of the product in the tin, i.e. before use, a shine that requires a lot of work, and inferior waterproofing of the treated leather. Moreover the amount of water in the products is typically less then 56.4% and the level of white spirit not lower than 22%. It is an object of the current invention to lower use of VOCs below 22% for emulsions.
The water continuous phase approach has led to several proposed solutions. The German patent application 35 41 434 discloses a shoe care product in the form of an emulsion containing wax, emulsifier, water and an anionic polysaccharide as co-emulsifier. Although this product is free of organic solvents, it has a cream-like consistency, which does not provide the wax layer of high gloss, which is desired of a shoe polish. The European patent application 1 000 990 discloses a water based shoe care product in the form of an emulsion containing wax, water and an emulsifier. In essence, the disclosed shoe care product is based on a specific, non-ionic emulsifier, viz. an alcohol having 6 to 28 carbon atoms alkoxylated with an alkene oxide having 2 to 4 carbon atoms. It has been found that this product does not give satisfactory results when applied to a leather surface.
Thus, there is, still a need in the art for a water-based low VOC shoe or leather care product, achieving as much the same results as fully solvent based paste polishes as possible. The problem clearly is to achieve a sufficiently hard product with ingredients that result in optimally soft films to create the desired combination of product properties
The applied and remaining polish film thickness after polishing of water continuous polish increases as compared to solvent based polish. This has negative effects on gloss level, gloss durability and gloss type. In order to reduce the resulting film thickness of water-based low VOC polishes, a balance between the film plasticity and hardness, inherent film adhesion capacity and film elasticity has to be struck. Addition of wax phase softening agents reduces the hardness of the product, which result in application of too high amounts of polish on the shoe. Too low plasticity of product particles in the product film results in a low removal of excess product, while too high film plasticity results in limited gloss durability. Too low inherent adhesive capacity result in near to complete removal of the film and consequently a low gloss product. Too high film adhesive capacity leads to thick films, which result in short gloss durability.